1. Field of the Invention
The present invention relates to a zoom lens suitable as, for example, a projector lens used for an image projection apparatus (i.e., a projector) that enlarges and projects an image on a screen.
2. Description of the Related Art
Various image projection apparatuses (i.e., projectors) that use image display elements, such as liquid crystal, enlarge and project an image in accordance with the image display elements on a screen surface through a projection optical system have been proposed. As a projection optical system used for a projector, a zoom lens capable of projecting at various projection magnifications and projecting at a wide view angle on a large screen from a short distance is demanded. Further, a zoom lens having a long back focus is demanded so that a color separation optical system, a color synthesis optical system and the like may be disposed between a projection optical system and image display elements.
As a zoom lens for a projector that is capable of projecting at a wide view angle and having a long back focus, a retro focus type zoom lens has been proposed (U.S. Patent No. 2007/0223103 A1 and Japanese Patent Application Laid-Open No. 2003-15038). U.S. Patent No. 2007/0223103 A1 discloses a zoom lens that is capable of projecting at a wide view angle and is constituted by 1st to 6th lens units having negative, positive, positive, positive, negative and positive refractive power sequentially from an enlargement conjugate side to a reduction conjugate side. During zooming, the 1st and the 6th lens units are not moved and the 2nd to the 5th lens units are moved.
Japanese Patent Application Laid-Open No. 2003-15038 discloses a zoom lens that is capable of projecting at a wide view angle and is constituted by 1st to 6th lens units having negative, positive, positive, negative, positive and positive refractive power sequentially from an enlargement conjugate side to a reduction conjugate side. During zooming, the 1st, the 4th and the 6th lens units are not moved and the 2nd, the 3rd and the 5th lens units are moved.